Calling SiriusXM an "extraordinary company with an incredible team," Karmazin — a cofounder of Infinity Broadcasting and former president and CEO of CBS who joined Sirius in 2004 — said he believed that the company's "best years are ahead."

"SiriusXM is an extraordinary company with an incredible team. It is an honor to come to work here every day where we truly deliver the best radio on radio. I am incredibly proud of what we have accomplished. Given where we started, it is amazing that SiriusXM has grown to become the largest radio company in the world," Karmazin said. "We continue to grow our subscriber base to record levels and our financial position has never been stronger. Importantly, the commitment to delivering innovative new products and technologies is very strong. SiriusXM has a strong foundation to build on for the future and there is a great team in place to keep the company moving forward. I am confident that SiriusXM's best years are ahead," said Karmazin."

"On behalf of the Board of Directors, I want to thank Mel for his significant contributions to the Company," said Eddy Hartenstein, SiriusXM's chairman of the board, said. "Thanks to Mel, we are well-positioned for long-term growth and value creation. We will miss Mel – and the Board wishes him the very best in his future endeavors – SiriusXM has a strong executive team in place and we are very confident in our business and our future prospects."

Sirius' board has launched a search comittee led by Greg Maffei to seek internal and external candidates for Karmazin's successor.